نشریه مهندسی برق
سال چهل و چهارم شماره 4 (پیاپی 70، زمستان 1393)

Insulation properties of oil have very important role in power system operation. Intensive care should therefore be taken in all aspects of its production and service. In recent researches, the effect of various additives on the transformer oil has been studied to achieve better technical and economical characteristics. In this paper, the effect of Carbon Nano Tubes on the transformer oil in power frequency test voltage is analyzed. The breakdown voltage and rate of rise of recovery voltage are two main quality measures of liquid insulation. Therefore, it is tried to compare these two parameters for pure oil and oil containing carbon Nano Tubes. Accordingly, the variations are analyzed and based on the physical properties of the test materials, it is tried to explain the phenomenon behind the changes. The results show, adding Carbon Nano Tubes despite the weakening of breakdown voltage at power frequency rate of insulation recovery is improved.

In this paper, a robust model predictive control (RMPC) is proposed based on model reference adaptive system (MRAS). In this algorithm, using the MRAS a combinational RMPC controller, which is called CRMPC, for three degree freedom satellite is designed such that the effect of moment of inertia uncertainty and external disturbance is compensated on the stability and performance of closed loop system. Control law is a state feedback which its gain is obtained by solving a convex optimization problem subject to several linear matrix inequalities (LMIs). To avoid the actuators saturation a linear matrix inequality is incorporated as LMI in the mentioned optimization problem. The advantages of this algorithm are needless to exact information from system’s model, robustness against model uncertainties and external disturbance. The proposed algorithm is implemented on the satellite attitude control system and the results of them are compared to generalized incremental model predictive control (GIPC) algorithm. The results show that the suggestive controller is more robust than the GIPC method.Keywords: Robust model predictive control; Linear matrix inequality; Model reference adaptive system; Satellite attitude control system.

A common attack in wireless sensor networks is the node replication attack. In this attack, attackers capture a number of nodes and spread copies of them in the network. Replicated nodes, which are controlled by the attackers, start communicating with other nodes to corrupt network protocols. In this paper we propose a new algorithm for detecting replica nodes in wireless sensor networks with mobile nodes using the legal wormhole channels. The proposed algorithm consists of two phases: local detection and global detection. In the first phase, each node detects replica nodes in its neighborhood by disseminating “Hello” messages. In the second phase few nodes in the network establish legal wormhole channels pairwise and exchange the information of their neighbors. When there is a common node in these neighbors, that node is known as a replica node. The experimental results show that the proposed algorithm outperforms similar algorithms in terms of detection rate and detection time.

In recent years, the penetration of distributed generation (DG) resources has been dramatically increased in modern power systems. Even though, the high penetration of DGs has negative impacts on the network performance, but the distribution network operators (DNOs) rarely intend to restrict them. Active management is an effective method of reinforcement network, accordance to the smart grid, for DG operation. This paper presents a multi-objective assessment model for distribution network in the presence of DGs and active management procedure. The proposed model not only discusses about the technical and economic objective function in distribution network but also evaluates the investment dynamic of the DG units. The positive role of active management on distribution network planning is presented. MATLAB software is used and the effect of applying the proposed model is shown on the sample distributed network.

The use of polymeric insulators in new lines and also updated power transmission lines is still growing. Polymeric insulators are exposed to various electrical, mechanical and environmental stresses. In many areas with cold weather, high voltage transmission lines and substations are vulnerable to freeze. The most important problems of these polymeric insulators, such as erosion and aging of polymeric materials, corona phenomena on insulator surface and flashover are related to the nonuniform potential distribution along the insulators. In this paper, electric field and voltage distribution of 230 kV polymeric insulator has been evaluated with and without corona ring in the presence of an ice layer on it. Electric field analysis software package, COMSOL Multiphysics4.2, based on the finite element method, has been employed for the calculations. Simulation results have shown a dramatic decrease in the intensity of the electric field in polymeric insulators in the presence of corona ring. Also the presence of air gap in the ice layer has a great influence on the potential distribution along the polymeric insulators and causes to increase intensity of the electric field on polymeric insulators surface.

3D pose estimation of players’ location is one of the challenging issues in the soccer video analysis. The soccer videos are generally captured using uncalibrated cameras, therefore the first step to calculate 3D pose of the players is the camera calibration and estimating its location. For the purpose of calibration, it is necessary to extract some 3D points and their image correspondence. Therefore, in the first stage of the proposed algorithm, we automatically extract points and the required data for calibration. Then a new method for camera calibration is proposed based on the coplanarity of the soccer field. The method uses coplanarity of points in soccer plane and their known location for camera calibration. We derive a closed form model to calculate different camera parameters. We compare the results of the proposed method with those of existing methods and results show the efficiency of the proposed algorithm.